Schlenk apparatus

Fig. 1. Modified Schlenk apparatus, front and side views.

Hydroxylamlne base has been prepared by the method of Lecher and Hofmann/ The free base can be stored in a tightly stoppered flask at -20°C for several days. The checkers found 1t expedient to prepare free hydroxylamine by a modification of the Lecher and Hofmann procedure in which a Schlenk tube under dry Ng was used to filter the NaCl precipitate and the NH20H base was crystallized from the filtrate at -30°C, then isolated by inverting the Schlenk apparatus and filtering the product (74% yield from the hydrochloride). 

G. Variations in Schlenk Ware. A large number of modifications of the basic Schlenk ware are in use. The double-ended filter is a commonly used variant of the standard Schlenk filter. The particular unit illustrated in Fig. 1.29 is equipped with O-ring joints rather than standard taper joints. (See Chapter 8 for a discussion of joints and O-ring materials.) Either conventional or modified O-ring joints, such as the Fischer and Porter Co. Solv-Seals, have several advantages over standard taper joints for Schlenk apparatus these O-joints are more resistant to solvents than the conventional standard taper ware, the O-joints are more readily clamped together, and, unlike standard taper joints, the two halves... 

Crystallization is performed in Schlenk apparatus under an inert atmosphere using familiar techniques partial removal of solvent by evacuation, addition of a solvent in which the solute has reduced solubility, and cooling. These methods are often combined for example, a second, poorer solvent, chosen so that its vapor pressure is less than that of the more powerful, original solvent, may be added. Partial evacuation will then concentrate the solution and change the solvent composition to favor crystallization. The complication which air-sensitive... 

Sublimation is readily performed in Schlenk apparatus of the type illustrated in Fig. 1.26. The sublimate, which collects on the upper walls, may be collected by positioning the apparatus horizontally and scraping the product into a receiver attached to the side joint while an inert-gas flush is maintained on the equipment. 

If the homogeneous product obtained is now allowed to stand undisturbed at a temperature of 0 to 10°C., some of the nitrogen complex precipitates. When a 100-ml. quantity of cold petroleum ether is added to the solution, an additional quantity of the solid orange complex is deposited. The solution is filtered under a nitrogen atmosphere by a Schlenk apparatus, as described in the preceding preparation (synthesis 2). The Schlenk filter is placed in the flask neck occupied by the con-... 

Schlenk apparatus (also called a Schlenk line) 597... 

All operations are carried out in a dry, inert atmosphere. Schlenk apparatus capable of handling ca. 500 mL of solution is useful for the work-up of the products. Although the intermediates may be handled briefly in air, bis(f/6-benzene)molybdenum is immediately decomposed by oxygen. 

The solvents are laboratory grade. Methanol and chloroform are distilled and stored under nitrogen before use. Sodium-dried tetrahydrofuran (THF) is redistilled over LiAlH4 under nitrogen before use. ( Caution. To minimize the chance of explosion, peroxide-free THF must be employed. See Reference 8 for details.) The aqueous solutions are carefully degassed in vacuo and saturated with nitrogen before use. Potassium hexachlororhodate(3-) monohydrate is prepared as described in the literature.4 The operations are carried out with the usual Schlenk apparatus.5... 

The synthesis must be carried out under a very pure nitrogen atmosphere (02 < 2 ppm in volume) using the Schlenk-apparatus technique.9 All the solvents and solutions are thoroughly degassed in vacuo and stored under nitrogen before use. The solvents are laboratory grade. Acetone and methyl formate are simply distilled, whereas benzene is refluxed and distilled over sodium. 

As is described here the transfer of solids is carried out in a nitrogen-flushed dry box, and the syntheses are performed in standard Schlenk apparatus under a nitrogen atmosphere.6 Alternatively, the entire synthesis may be performed in an inert-atmosphere dry box. 

A Schlenk apparatus was charged with the briefly sonicated Step 1 product dispersed in DMSO and treated with the drop wise addition of 10 ml of a lOmM solution of Wilkinson s complex in DMSO. The reaction mixture was stirred at 55°C to 60°C for 80 hours and filtered through a 0.2 pm nylon membrane. Dissolved tubes were precipitated out by treating the solution with saturated brine. The precipitated material was purified by filtering over a 0.2 pm nylon membrane and washing in DMSO, ethanol, and water. 

A Schlenk apparatus, illustrated in Fig. 3 and similar to that employed by Collman et al., is used for the reaction sequence. Vacuum and argon sources are provided by a double manifold, to which the stopcocks of the apparatus are attached. Prepurified nitrogen can be used in place of argon. 

Imidazole quaternary salts (9) are frequently quite hygroscopic and need to be kept dry if storage is intended. In their synthesis all apparatus must be scrupulously dry, solvents must be dried before use, and reactions and recrystallizations need to be carried out under dry nitrogen. Liquid reagents are best added using a syringe through a serum cap, and Schlenk apparatus is recommended for filtrations. 

To a solution of 1-methylimidazole (3.28 g, 40 mmol) in freshly distilled THE (50 ml) cooled to -10°C is added a solution of n-butyllithium (40 mmol) in hexane (25 ml) over 1 h. The solution is kept at - 10°C and stirred (1 h) before adding a solution of trimethyltin chloride (40 ml) in diethyl ether (50 ml) over 1 h via a syringe. The mixture is allowed to warm to room temperature, filtered using conventional Schlenk apparatus, and the solvents are removed under reduced pressure. The product is isolated by distillation (10.79 g, 73%), bo.s 84-86 C. 

All of the following operations are performed in a nitrogen-flushed dry box or in standard Schlenk apparatus under pure, dry nitrogen atmosphere.2... 

All manipulations are conveniently accomplished using a standard Schlenk apparatus. Tetrahydrofuran (THF) is refluxed over sodium/benzophenone until dry, then distilled under nitrogen prior to use. Dichloromethane is stirred over KOH, then distilled from P4Ol0. Ethanol is degassed using freeze-pump-thaw cycles, and is then stored over molecular sieves. 

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